As one of methods for downsizing a liquid crystal display device and reducing power consumption of the same, there has been known a method of integrally forming pixel circuits and drive circuits of the pixel circuits on a same substrate. Hereinafter, the liquid crystal display device configured by this method will be referred to as a “driver-integrated liquid crystal display device”. In the driver-integrated liquid crystal display device, the drive circuits are configured using thin film transistors (hereinafter, referred to as TFT (s)) made of low-temperature polysilicon, CG silicon (Continuous Grain silicon) or the like.
FIG. 7 is a block diagram showing a configuration of a conventional driver-integrated liquid crystal display device. The liquid crystal display device shown in FIG. 7 includes a liquid crystal panel 81 in which pixel circuits 82, a gate driver circuit 83, and a source driver circuit 84 are integrally formed on a glass substrate. The source driver circuit 84 includes a shift register 85, a D/A conversion circuit 86, a buffer circuit 87 and a sampling gate 88. The buffer circuit 87 drives a source line SL connected to the pixel circuit 82, based on an analog voltage Vin outputted from the D/A conversion circuit 86. The sampling gate 88 makes switching as to whether or not the buffer circuit 87 and the source line SL are to be connected. The sampling gate 88 is provided to disconnect the source line
SL from the buffer circuit 87 and keep a voltage of the source line SL constant. Moreover, the sampling gate 88 is used to switch and drive the plurality of source lines SL. Switching and driving the plurality of source lines SL can decrease the D/A conversion circuits 86 and the buffer circuits 87 than the source lines SL in number.
FIG. 8 is a circuit diagram showing a part at subsequent stages of the D/A conversion circuit 86 of the liquid crystal display device shown in FIG. 7. In a circuit shown in FIG. 8, the buffer circuit 87 is configured using an operational amplifier 89. To a positive-side input terminal of the operational amplifier 89 is applied the analog voltage Vin outputted from the D/A conversion circuit 86. An output terminal of the operational amplifier 89 is feedback connected to a negative-side input terminal thereof. The operational amplifier 89 functions as a unity gain amplifier and makes control so that the voltage of the source line SL is equal to the analog voltage Vin.
FIG. 9 is a circuit diagram showing one example of the operational amplifier 89. The operational amplifier 89 shown in FIG. 9 includes TFTs M1 to M7 and a capacitor C1, and applies A class amplification to differential input voltages Vin+ and Vin− to generate an output voltage Vout. Performing the A class amplification in the operational amplifier 89 allows the source line SL to be driven based on the output voltage Vout with small distortion.
A technique relating to the invention of the present application is also described in the following documents. In Patent Document 1, an output stage circuit of a source driver circuit shown in FIG. 10 is described. The output stage circuit shown in FIG. 10 performs a three-stage operation of initial setting, writing and retaining in accordance with a timing chart shown in FIG. 11. States of switches SW7 to SW10 are changed in accordance with a high level or a low level of an output of a comparison circuit 92. In Patent Documents 2 to 4, other examples of the source driver circuit that drives the source line based on the input voltage are described.